This invention relates to data recording and recovery systems, and particularly to magnetic data storage and retrieval systems.
Run length limited codes have gained significant recognition in magnetic data storage systems due to their ability to increase density of stored data over other forms of code One such code is the (1,7,2,3) code (shortly 1,7 code), which has a minimum of 1 encoded zero between successive encoded ones and a maximum of 7 encoded zeroes between successive encoded ones, and it has a rate of 2/3, that is, source bits encoded into 3 code bits. The advantages of (1,7,2,3) type codes are described by T. Horiguchi and K. Morita, "An Optimization of Modulation Codes in Digital Recording", IEEE Transactions on Magnetics, Vol. MAG-12, pp. 740-742, Nov. 1976; G. Jacoby and R. Kost, "Binary Two-Thirds Rate Code with Full Word Look-Ahead", IEEE Transactions on Magnetics, Vol. MAG-20, pp. 709-714, Sept. 1984; P. H. Siegel, "Recording Codes for Digital Magnetic Storage", IEEE Transactions on Magnetics, Vol. MAG-21, pp. 1344-1349, September 1985. See also Cohn et al, U.S. Pat. No. 4,337,458, issued June 29, 1982.
The aforementioned Minuhin application describes an efficient self-synchronizing encoding/decoding scheme for 1,7 code. The present invention concerns a self-initialization scheme which demonstrates an extremely low sensitivity to errors in the preamble of the record. The preamble comprises a synchrofield, which is necessary for the operation of the readback phase locked loop (PLL), and a synchrobyte, which locates the beginning of the stored message. It is the practice of the industry that errors in the preamble are not corrected by the error correction codes (ECC). Hence, there exists a significant probability of incorrect decoder initialization and a loss of an entire record due to errors in the preamble, especially in the case of high density recording which is allowed by and dependent on ECC.
It is, therefore, an object of the present invention to provide an efficient self-initialization scheme for a 1,7 code decoder which is not susceptible to errors in the synchrofield of the record.
Another object of the present invention is to provide an initialization scheme for a 1,7 code decoder which is not dependent on correct synchrobyte detection.
It is still another object of the present invention to provide a flexible 1,7 code decoder which can operate with a custom defined synchrobyte(s).